The invention relates to improvements in swivels for connecting utility products to pipe strings in horizontal directional drilling operations.
Horizontal direction drilling is increasingly popular because of increased demand for placement of utility product such as communications cable, power cable or conduit, infrastructure that obstructs traditional trenching methods, and technological advances in horizontal directional drilling. Activity in this field has demonstrated a need for a reliable coupling device to connect a drill or pipe string to a product line such as conduit for fiber optic cable. Typically, the product is installed by pulling the drill or pipe string back through the bore that has been created by various drilling and reaming methods. Coupling devices, commonly known as swivels, have been introduced to the industry. These swivels are intended to allow a pipe string to rotate while pulling the product without requiring the product to rotate. Rotation of the product could damage it. Existing swivel designs are prone to failure because of the harsh environment and high forces that are experienced in typical product installations. More specifically, the bore may be exposed to drilling fluid such as a mixture of water, bentonite and polymers known in the industry as xe2x80x9cmudxe2x80x9d. This liquid is used as coolant for the cutting tools, holding the drilled hole or bore open and to lubricate the product being installed.
This liquid or mud can be destructive of the bearing seals and bearings typically found in commercially available swivels. Bearings may fail, not only from degradation or loss of lubrication due to seal failure, but also from heavy bending force loads on the swivel which the bearing structure is not capable of sustaining. Another significant problem with prior art swivels is their tendency to break under combined cyclic tensile and bending stresses that typically occur in use. These bending forces occur as the pipe string, swivel and product pass along a bore that deviates from a straight line such as where a hard formation or other obstruction or resistance may have been encountered during drilling operations. The nature of the work limits the physical size of the componentry in a swivel making it difficult to achieve satisfactory strength and durability.
The invention provides a swivel for use with horizontal directional drilling equipment for product installation that has improved performance, durability and maintenance characteristics. A swivel constructed in accordance with the invention has extended bearing life by inclusion of a type of bearing assembly that tolerates practical dimensional tolerances and inevitable bending deflections in the swivel components during use. The swivel incorporates a metal face seal between the rotating and non-rotating parts of the swivel to exclude solid and liquid contaminanats from the interior and to retain lubricant therein.
A cantilever or stub shaft supporting the bearing structure in the swivel has a large smooth fillet at its base to significantly reduce stress riser effects at this cross-section transition area. This area is capable of sustaining substantial tensile and compressive forces as well as large cyclical bending forces without failure in an extended service life. The swivel achieves a desired compactness by arranging the seal assembly around the shaft transition area. These elements, consequently, do not separately add to the necessary length of the swivel. Moreover, the seal assembly uses parts of the structure of the swivel itself to eliminate the need to make an outside diameter of the swivel larger than is required. The disclosed swivel is retained in an assembled state by a unique welding technique that is simple, reliable and avoids complicated and/or tedious labor when the swivel is disassembled and reassembled for regular maintenance and/or inspection and refurbishment.